Apparatus and method  for supporting transmission of sounding reference signals from multiple antennas

ABSTRACT

Methods and apparatuses, through the use of a Downlink Control Indication (DCI) format or through higher layer signaling, for dynamic activation and deactivation of Sounding Reference Signal (SRS) transmissions from User Equipments (UEs) in an UL Component Carrier (CC) with configured SRS transmissions, the dynamic configuration of SRS transmissions parameters, the dynamic activation and configuration of SRS transmissions in an UL CC without previously configured SRS transmissions for a reference UE, and the configuration of SRS transmissions from multiple UE transmitter antennas.

PRIORITY

The present application is a Continuation Application of U.S.application Ser. No. 12/568,351, which was filed in the U.S. Patent andTrademark Office on Sep. 28, 2009, and claims priority under 35 U.S.C.§119(e) to U.S. Provisional Application No. 61/100,449, entitled“Transmission of Sounding Reference Signals”, which was filed on Sep.26, 2008, the contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a wireless communicationsystem and, more particularly, to the transmission of sounding referencesignals from multiple transmitter antennas of a user equipment. Thesounding reference signals are intended to provide, among otherobjectives, an estimate of the channel medium experienced by the signalfrom each transmitter antenna. The present invention is also directed tosupporting the transmission of sounding reference signals in multipledistinct bandwidths of a communication system.

2. Description of the Art

In order for a communication system to function properly, several typesof signals are supported by the communication system. In addition todata signals, which convey information content, control signals alsoneed to be transmitted to enable proper processing of the data signals.Such signals are transmitted from User Equipments (UEs) to their servingBase Station (BS or Node B) in the UpLink (UL) of the communicationsystem and from the serving Node B to the UEs in the DownLink (DL) ofthe communication system. Examples of control signals include positiveor negative acknowledgement signals (ACK or NAK, respectively) that aretransmitted by a UE in response to correct or incorrect data packetreception. Control signals also include Channel Quality Indication (CQI)signals, which are sent by a UE to the Node B to provide informationabout DL channel conditions that UE experiences. Reference Signals (RS),also known as pilots, are typically transmitted by each UE to eitherenable coherent demodulation for transmitted data or control signals atthe Node B or, in the UL, to be used by the receiving Node B to measureUL channel conditions that the UE experiences. An RS that is used fordemodulation of data or control signals is referred to as a Demodulation(DM) RS, while an RS that is used for sounding the UL channel medium,and which is typically wideband in nature, is referred to as a SoundingRS (SRS).

A UE, also commonly referred to as a terminal or a mobile station, maybe fixed or mobile and may be a wireless device, a cellular phone, apersonal computer device, etc. A Node B is generally a fixed station andmay also be referred to as a Base Transceiver System (BTS), an accesspoint, or some other terminology.

UEs transmit signals conveying data or control information through aPhysical Uplink Shared CHannel (PUSCH) while, in the absence of PUSCHtransmission, the UEs transmit control signals through a Physical UplinkControl CHannel (PUCCH). A UE receives signals conveying datainformation through a Physical Downlink Shared CHannel (PDSCH), while DLcontrol signals are conveyed through a Physical Downlink Control CHannel(PDCCH).

The UEs are assumed to transmit data or control signals over aTransmission Time Interval (TTI) which may correspond to a sub-framehaving a duration of 1 millisecond (msec), for example.

FIG. 1 illustrates a block diagram of a sub-frame structure 110 forPUSCH transmission. The sub-frame includes two slots. Each slot 120includes seven symbols used for the transmission of data and/or controlsignals. Each symbol 130 further includes a Cyclic Prefix (CP) in orderto mitigate interference due to channel propagation effects. Somesymbols in each slot may be used for RS transmission 140 to providechannel estimation and to enable coherent demodulation of a receivedsignal. It is also possible for the TTI to have only a single slot or tohave more than one sub-frame. The transmission BandWidth (BW) is assumedto include frequency resource units, which are referred to herein asResource Blocks (RBs). For example, each RB includes N_(sc) ^(RB)=12sub-carriers. UEs may be allocated one or more consecutive RBs 150 forPUSCH transmission and one RB for PUCCH transmission. The above valuesare for illustrative purposes only.

PUSCH transmission or PDSCH reception by a UE may be initiated by thereception of a corresponding Scheduling Assignment (SA) at the UE, whichwas transmitted by the Node B through a Downlink Control Information(DCI) format in the PDCCH. The DCI format may inform a UE about a datapacket transmission by the Node B in the PDSCH (DL SA), or about a datapacket transmission to the Node B (UL SA) in the PUSCH. The Node B isassumed to separately code and transmit each DCI format conveying a SA.

FIG. 2 illustrates a processing chain at the Node B for an SAtransmission. The Medium Access Control (MAC) UE IDentity (UE ID), forthe UE that the SA is intended for, masks the CRC of the SA codeword.This enables the reference UE to identify that the SA is intended forit. A CRC of (non-coded) SA bits 210 is computed at block 220 and thenmasked using an exclusive OR (XOR) operation 230 between CRC bits and aMAC UE ID 240. Specifically, XOR(0,0)=0, XOR(0,1)=1, XOR(1,0)=1,XOR(1,1)=0. The masked CRC is then appended to the SA bits in block 250,and channel coding, such as for example convolutional coding, isperformed in block 260. In block 270 rate matching to the allocatedPDCCH resources is performed, and interleaving and modulation areperformed in block 280, before transmission of a respective controlsignal 290.

The UE receiver performs the reverse operations of the Node Btransmitter to determine whether it has an SA. These operations areillustrated in FIG. 3. A received control signal 310 is demodulated andthe resulting bits are de-interleaved in block 320. The Node B ratematching is restored in block 330, followed by decoding in block 340. SAbits 360 are then obtained after extracting CRC bits in block 350 whichare then de-masked by applying an XOR operation 370 with a UE ID 380.Finally, the UE performs a CRC test in block 390. If the CRC test ispassed, the UE considers the SA as valid and determines the parametersfor signal reception (DL SA) or signal transmission (UL SA). If the CRCtest is not passed, the UE disregards the presumed SA.

A UL SA DCI format is described with respect to Table 1. Table 1provides information about at least some of the Information Elements(IEs) an UL SA DCI format typically contains. Additional IEs or adifferent number of bits for each indicative IE in Table 1 may apply.The order with which IEs appear in an UL SA DCI format is arbitrary.

TABLE 1 IEs of an UL SA DCI format for PUSCH Transmission. IE Number ofBits Comment Resource Allocation 11 Assignment of Consecutive RBs (Totalof 50 RBs) TBS (MCS) 5 MCS Levels NDI 1 New Data Indicator (synchronousUL HARQ) TPC 2 Power control commands Cyclic Shift Indicator 3 SDMA(maximum of 8 UEs) Hopping Flag 1 Frequency Hopping (Yes/No) CQI Request1 Include CQI report (Yes/No) CRC (UE ID) 16 UE ID masked in the CRCTOTAL 40

The first IE provides RB allocation. The UL signal transmission methodis assumed to be Single Carrier Frequency Division Multiple Access(SC-FDMA). With SC-FDMA, the signal transmission BW is contiguous. Foran operating BW of N_(RB) ^(UL) RBs, the number of possible contiguousRB allocations to a UE is 1+2+ . . . +N_(RB) ^(UL)=N_(RB) ^(UL)(N_(RB)^(UL)+1)/2 and can be signaled with |log₂(N_(RB) ^(UL)(N_(RB)^(UL)+1)/2)| bits, where ┌ ┐ denotes the ceiling operation which roundsa number to its next higher integer. Therefore, for N_(RB) ^(UL)=50, theIE requires 11 bits. Regardless of the transmission method, the UL SADCI format is assumed to contain an IE for resource allocation.

The second IE provides Modulation and Coding Scheme (MCS) or TransportBlock Size (TBS). With 5 bits, a total of 32 MCS or TBS can besupported. For example, the modulation may be QPSK, QAM16, or QAM64while the coding rate may take discrete values between, for example,1/16 and 1. Using the resource allocation information, a UE candetermine the TBS from the MCS, or the reverse. Some MCS IE values maybe used in conjunction with the application of Hybrid Automatic RepeatreQuest (HARQ) as is subsequently described.

The third IE is a New Data Indicator (NDI). The NDI is set to 1 if a newtransport block should be transmitted, and is set to 0 if the sametransport block, as in a previous transmission, should be transmitted(synchronous UL HARQ is assumed in this example).

The fourth IE provides a Transmission Power Control (TPC) command forpower adjustments to the transmitted PUSCH signal and SRS signal.

The fifth IE is a Cyclic Shift (CS) indicator enabling the use of adifferent CS for a Constant Amplitude Zero Auto-Correlation (CAZAC)sequence used for the DM RS transmission in the PUSCH. As issubsequently described, the use of a different CS by a different UEs canprovide orthogonal multiplexing of the respective RS.

The sixth IE indicates whether the PUSCH transmission hops in frequency.

The seventh IE indicates whether a DL CQI report should be included inthe PUSCH.

In order for the Node B to properly determine the RBs and MCS for PUSCHtransmission from a UE, it requires a UL CQI estimate over at least apart of the operating BW. Typically, this UL CQI estimate is obtained bythe UE transmitting an SRS over the scheduling BW. The SRS istransmitted in one or more UL sub-frame symbols, replacing transmissionof data or control. In addition to providing a Signal-to-Interferenceand Noise Ratio (SINR) estimate over its transmission BW, the SRS canalso serve for UL TPC and UL synchronization.

FIG. 4 shows an SRS transmission. The SRS transmission occurs in a lastsub-frame symbol of every other sub-frame 460, 465, for a respective4.3% SRS overhead. UE1 410 and UE2 420 multiplex their PUSCHtransmissions in different parts of the operating BW during a firstsub-frame 401, while UE2 420 and UE3 430 do so during a second sub-frame402, and UE4 440 and UE5 450 do so during a third sub-frame 403. In someUL sub-frame symbols, UEs transmit DM RSs to enable the Node B receiverto perform coherent demodulation of the data or control signaltransmitted in the remaining sub-frame symbols. For example, UE1, UE2,UE3, UE4, and UE5 transmit DM RS 415, 425, 435, 445, and 455,respectively. UEs with SRS transmission may or may not have PUSCHtransmission in the same sub-frame and, if they co-exist in the samesub-frame, SRS and PUSCH transmissions may be located at different partsof the operating BW.

The RS (DM RS or SRS) is assumed to be constructed from CAZAC sequences.An example of such sequences is given by the following Equation (1):

$\begin{matrix}{{c_{k}(n)} = {\exp \left\lbrack {\frac{{j2\pi}\; k}{L}\left( {n + {n\frac{n + 1}{2}}} \right)} \right\rbrack}} & (1)\end{matrix}$

where L is a length of the CAZAC sequence, n is an index of a sequenceelement, n={0, 1, 2 . . . , L−1}, and k is a sequence index. For CAZACsequences of prime length L, the number of sequences is L−1. Therefore,an entire family of sequences is defined as k ranges in {1, 2 . . . ,L−1}. However, the sequences for RS transmission need not be generatedby strictly using the above expression. As 1 RB is assumed to includeN_(sc) ^(RB)=12 sub-carriers, the sequences used for RS transmission canbe generated by either truncating a longer prime length (such as length13) CAZAC sequence or by extending a shorter prime length (such aslength 11) CAZAC sequence by repeating its first element(s) at the end(cyclic extension), although the resulting sequences do not strictlyfulfill the definition of a CAZAC sequence. Alternatively, CAZACsequences can be generated through a computer search for sequencessatisfying the CAZAC properties.

FIG. 5 shows a transmitter structure for the DM RS or the SRS based on aCAZAC sequence. The frequency domain version of a CAZAC sequence may beobtained by applying a Discrete Fourier Transform (DFT) to its timedomain version. By choosing non-consecutive sub-carriers, a combspectrum can be obtained for either the DM RS or the SRS. A combspectrum is useful for orthogonally multiplexing (through frequencydivision) overlapping SRS transmissions with unequal BWs. Such SRSs areconstructed by CAZAC sequences of different lengths, which cannot beorthogonally multiplexed using different CS.

Referring to FIG. 5, a frequency domain CAZAC sequence 510 is generated,the sub-carriers in the assigned transmission BW are mapped in block 520through control of transmission bandwidth in block 530, the Inverse FastFourier Transform (IFFT) is performed in block 540, the CS is applied inblock 550, the CP is applied in block 560 and filtering is applied intime windowing block 570 to a transmitted signal 580. The UE applies nopadding in sub-carriers in which the DM RS or the SRS is nottransmitted, such as in sub-carriers used for signal transmission byanother UE and in guard sub-carriers (not shown). Additional transmittercircuitry such as a digital-to-analog converter, analog filters,amplifiers, and transmitter antennas, as they are known in the art, arenot shown.

At the receiver, the inverse (complementary) transmitter functions areperformed. This is conceptually illustrated in FIG. 6 where the reverseoperations of those in FIG. 5 apply. In FIG. 6, an antenna receives aRadio-Frequency (RF) analog signal and after passing through furtherprocessing units (such as filters, amplifiers, frequencydown-converters, and analog-to-digital converters) a resulting digitalreceived signal 610 passes through a time windowing unit 620 and the CPis removed in block 630. Subsequently, the CS of the transmittedCAZAC-based sequence is restored in block 640, a Fast Fourier Transform(FFT) is applied in block 650, the selection of the transmittedsub-carriers is performed in block 665 through control of receptionbandwidth in block 660, and correlation with a CAZAC-based sequencereplica 680 is applied at multiplier 670. Finally, output 690 isobtained and can then be passed to a channel estimation unit, such as atime-frequency interpolator, or an UL CQI estimator.

Different CSs of a CAZAC sequence provide orthogonal sequences.Therefore, different CSs of a CAZAC sequence can be allocated todifferent UEs and achieve orthogonal multiplexing of the RS transmittedby these UEs in the same RBs. This principle is illustrated in FIG. 7.In order for multiple CAZAC sequences 710, 730, 750, and 770, generatedrespectively from multiple CSs 720, 740, 760, and 780, of the same rootCAZAC sequence to be orthogonal, CS value Δ 790 should exceed thechannel propagation delay spread D (including a time uncertainty errorand filter spillover effects). If T_(S) is the duration of one symbol,the number of CSs is equal to the mathematical floor of the ratioT_(S)/D.

The SRS transmission BW may depend on a UL SINR that the UE experiences.For UEs with low UL SINR, the Node B may assign a small SRS transmissionBW in order to provide a relatively large ratio of transmitted SRS powerper BW unit, thereby improving the quality of the UL CQI estimateobtained from the SRS. Conversely, for UEs with high UL SINR, the Node Bmay assign a large SRS transmission BW since good UL CQI estimationquality can be achieved from the SRS while obtaining this estimate overa large BW.

Several combinations for the SRS transmission BW may be supported asshown in Table 2, which corresponds to configurations adopted in 3GPPE-UTRA LTE. The Node B may signal a configuration c through a broadcastchannel. For example, 3 bits can indicate one of the eightconfigurations. The Node B may then individually assign to each UE oneof the possible SRS transmission BWs m_(SRS,b) ^(c) (in RBs) byindicating the value of b for configuration c. Therefore, the Node B canmultiplex SRS transmissions from UEs in the BWs m_(SRS,0) ^(c),m_(SRS,1) ^(c), m_(SRS,2) ^(c), and m_(SRS,3) ^(c) (b=0, b=1, b=2, andb=3, respectively in Table 2).

TABLE 2 Example of m_(SRS,b) ^(c) RB values for UL BW of N_(RB) ^(UL)RBs with 80 < N_(RB) ^(UL) ≦ 110. SRS BW configuration b = 0 b = 1 b = 2b = 3 c = 0 96 48 24 4 c = 1 96 32 16 4 c = 2 80 40 20 4 c = 3 72 24 124 c = 4 64 32 16 4 c = 5 60 20 Not 4 Applicable c = 6 48 24 12 4 c = 748 16  8 4

Variation in the maximum SRS BW is primarily intended to accommodate avarying PUCCH size. The PUCCH is assumed to be transmitted at the twoedges of the operating BW and to not be overlapped (interfered) with theSRS. Therefore, the larger the PUCCH size (in RBs), the smaller themaximum SRS transmission BW.

FIG. 8 further illustrates the concept of multiple SRS transmission BWsfor configuration c=3 from Table 2. The PUCCH is located at two edges,802 and 804, of the operating BW and a UE is configured SRS transmissionBWs with either m_(SRS,0) ³=72 RBs 812, or m_(SRS,1) ³=24 RBs 814, orm_(SRS,2) ³=12 RBs 816, or m_(SRS,3) ³=4 RBs 818. A few RBs, 806 and808, may not be sounded, but this usually does not affect the ability ofthe Node B to schedule PUSCH transmissions in those RBs, since therespective UL SINR may be interpolated from nearby RBs with SRStransmission. For SRS BWs other than the maximum, the Node B alsoassigns to a UE a starting frequency position of the SRS transmission.

The SRS transmission parameters are assumed to be configured for each UEby the Node B through higher layer signaling, for example, through theMAC layer or the Radio Resource Control (RRC) layer, and remain validuntil re-configured again through higher layer signaling. These SRStransmission parameters may include:

the SRS transmission BW

the SRS starting BW position

the SRS transmission comb (if the SRS has a comb spectrum)

the SRS CS

the SRS transmission period (for example, one SRS transmission every 5sub-frames)

the starting sub-frame of SRS transmission (for example, the firstsub-frame in a set of 1000 sub-frames)

whether SRS hopping is enabled (SRS transmission hops in the operatingBW or not).

The configuration of the SRS transmission parameters for each UE shouldbe such that

UL throughput gains are maximized while the SRS overhead is minimized.For example, a short SRS transmission period may only result inincreased UL overhead if the channel remains highly correlated betweentwo successive SRS transmissions. Conversely, a long SRS transmissionperiod may not provide the Node B with the proper UL CQI in sub-framesbetween two SRS transmissions for which the channel may become highlyuncorrelated.

Enabling high UL data rates and high UL spectral efficiencies requiresthe use of multiple UE transmitter antennas and the application ofSingle-User Multiple-Input Multiple-Output (SU-MIMO) methods. To obtainthe potential benefits from SU-MIMO, the Node B scheduler should beprovided with a channel estimate from each UE transmitter antenna.Therefore, an SRS transmission from each UE transmitter antenna isrequired. Moreover, since the use of SU-MIMO is often associated with arelatively high UL SINR, the SRS transmission BW from each UEtransmitter antenna may be large. This reduces the SRS multiplexingcapacity and results in increased UL overhead. Considering that a UE mayhave as many as four or even eight transmitter antennas, the UL overheadrequired to support SRS transmissions may become too large and offset asignificant part of the SU-MIMO spectral efficiency gains.

Configuring the SRS transmission parameters to remain constant over along time period may often result in underutilization of the respectiveoverhead. When the UE has no data to transmit, and hence is notscheduled by the Node B, relatively frequent SRS transmissions arewasteful. When the UE has a large amount of data to transmit, and henceit often needs PUSCH scheduling, frequent SRS transmissions arerequired. However, this is not possible with a semi-static configurationof the SRS transmission parameters through higher layer (MAC or RRC)signaling without incurring prohibitive SRS overhead. Such conditionstypically occur for services associated with traffic bursts, such as,for example, file uploading or web browsing. Fast activation of SRStransmissions and fast configuration of the SRS transmission parametersenabled through dynamic physical layer control signaling are beneficialto address such traffic models while maintaining low SRS overhead.

A dynamically configured function is one enabled through physical layercontrol signaling, such as for example through a DCI format, while asemi-statically configured function is one enabled through higher layer(MAC or RRC) signaling. Physical layer signaling allows for fast UEresponse in the order of a sub-frame period. Higher layer signalingresults in slower UE response in the order of several sub-frame periods.

For a communication system having multiple UL Component Carriers (CCs),SRS transmission from a UE is assumed to be configured (through higherlayer signaling) only in those UL CCs with a respective PUSCHtransmission. In such cases, it is beneficial to also enable the Node Bto perform, dynamic or semi-static, activation and configuration of SRStransmissions in new UL CCs where the UE is not configured PUSCH or SRStransmission. This allows the Node B to obtain information for theinterference and channel conditions the UE will experience in the new ULCCs. Based on this information, the Node B may subsequently decide toalso schedule PUSCH transmissions from the UE in the new UL CCs, replacean existing UL CC with a new UL CC (discontinue scheduling in anexisting UL CC and begin scheduling in the new UL CC), or make no changeto the existing configuration of UL CCs.

SUMMARY OF THE INVENTION

The present invention has been made to address at least the aboveproblems and/or disadvantages and to provide at least the advantagesdescribed below. Accordingly, an aspect of the present inventionprovides methods and apparatus for dynamic activation of SoundingReference Signal (SRS) transmissions from User Equipments (UEs) in theUpLink (UL) of a communication system, for dynamic configuration of theSRS transmission parameters, for activation and configuration of SRStransmissions in component carriers not having configured SRStransmission from a reference UE, and for configuration of SRStransmission parameters from multiple UE transmitter antennas.

According to an aspect of the present invention, a method and anapparatus are provided for activating a Reference Signal (RS)transmission from a User Equipment (UE) in a communication system inwhich a base station transmits a Downlink Control Information (DCI)format conveying a Scheduling Assignment (SA) to the UE. The DCI formathas Information Elements (IEs) configuring a packet transmission fromthe UE to the base station or from the base station to the UE. The IEshave binary elements. The RS transmission has predetermined parametersindependent of the DCI format IEs. An “RS Activation” IE comprising atleast one binary element in the DCI format is configured by the UE. TheRS transmission is suspended by the UE, when the at least one binaryelement of the “RS Activation” IE has a first value. The RS istransmitted by the UE, when the at least one binary element of the “RSActivation” IE has a second value.

According to another aspect of the present invention, a method and anapparatus are provided for activating a Reference Signal (RS)transmission from a User Equipment (UE) in a communication system inwhich a base station transmits a Downlink Control Information (DCI)format conveying a Scheduling Assignment (SA) to the UE. The DCI formathas Information Elements (IEs) configuring a packet transmission fromthe UE to the base station or from the base station to the UE. The IEshave binary elements. The RS transmission has predetermined parametersindependent of the DCI format IEs. The DCI format is interpreted asconveying an SA to the UE, when binary elements of an IE convey a firstvalue comprised in a first set of values. The DCI format is interpretedas activating the RS transmission from the UE, when the binary elementsof the IE convey a second value comprised in a second set of values. Thefirst set of values and the second set of values are mutually exclusive.

According to a further aspect of the present invention, a method isprovided for configuring transmission parameters of a Reference Signal(RS) from a User Equipment (UE) in a communication system in which abase station transmits a Downlink Control Information (DCI) formatconveying a Scheduling Assignment (SA) to the UE. The DCI format hasInformation Elements (IEs) configuring a packet transmission from the UEto the base station or from the base station to the UE. The IEs havebinary elements. An “RS Activation” IE comprising at least one binaryelement is included in the DCI format. The DCI format is interpreted asconveying an SA to the UE, when the at least one binary element of the“RS Activation” IE has a first value. The DCI format is interpreted asconfiguring the transmission parameters of the RS when the at least onebinary element of the “RS Activation” IE has a second value.

According to an additional aspect of the present invention, a method isprovided for configuring transmission parameters of a Reference Signal(RS) from a User Equipment (UE) in a communication system in which abase station transmits a Downlink Control Information (DCI) formatconveying a Scheduling Assignment (SA) to a User Equipment (UE). The DCIformat has Information Elements (IEs) configuring a packet transmissionfrom the UE to the base station or from the base station to the UE. TheIEs have binary elements. The DCI format is interpreted as conveying anSA to the UE, when binary elements of an IE convey a first valuecomprised in a first set of values. The DCI format is interpreted asconfiguring the transmission parameters of the RS, when the binaryelements of the IE convey a second value comprised in a second set ofvalues. The first set of values and the second set of values aremutually exclusive.

According to another aspect of the present invention, in a communicationsystem having a set of Component Carriers (CCs) for transmission ofsignals from User Equipments (UEs) to a base station, wherein a UE isassigned by the base station a first subset of the set of CCs for thetransmission of signals conveying data information, a method andapparatus are provided for enabling the base station to configure the UEto transmit a signal conveying data information in at least oneadditional CC not belonging to the first subset of the set of CCs. Thetransmission of a Reference Signal (RS) from the UE in the at least oneadditional CC is configured by the base station. The RS is transmittedby the UE in the at least one additional CC.

According to a further aspect of the present invention, in acommunication system having a set of Component Carriers (CCs) fortransmission of signals from User Equipments (UEs) to a base station,wherein a UE is assigned by the base station a first subset of the setof CCs for the transmission of signals conveying data information, amethod and apparatus are provided for configuring parameters for aReference Signal (RS) transmission in a first CC belonging to the firstsubset of CCs and in a second CC not belonging to the first subset ofthe set of CCs. A first subset of a set of RS transmission parameters isconfigured in the first CC by the base station. A second subset of theset of RS transmission parameters is configured in the second CC by thebase station.

According to an additional aspect of the present invention, in acommunication system in which a User Equipment (UE) communicates with abase station, the UE having a set of transmitter antennas, a method isprovided for configuring a set of parameters for transmission of aReference Signal (RS) from a subset of the set of UE transmitterantennas. The base station configures a subset of the set of parametersfor RS transmission from a reference UE transmitter antenna in the setof transmitter antennas. A corresponding subset of the set of parametersfor the RS transmission from remaining transmitter antennas in the setof transmitter antennas is determined, by the base station, from thesubset of the set of parameters for the RS transmission from thereference UE transmitter antenna in the set of transmitter antennas.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of the presentinvention will be more apparent from the following detailed descriptionwhen taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a diagram illustrating a UL sub-frame structure for PUSCHtransmission in the UL of the communication system;

FIG. 2 is a block diagram illustrating the coding process of an SA atthe Node B;

FIG. 3 is a block diagram illustrating the decoding process of an SA atthe UE;

FIG. 4 is a diagram illustrating an SRS multiplexing method in the ULsub-frame structure;

FIG. 5 is a block diagram illustrating an RS transmitter structure;

FIG. 6 is a block diagram illustrating an RS receiver structure;

FIG. 7 is a diagram illustrating orthogonal RS multiplexing usingdifferent cyclic shifts of a CAZAC sequence;

FIG. 8 is a diagram illustrating a configuration for multiplexing SRStransmissions in various bandwidths; and

FIG. 9 is a diagram illustrating a UE decision process for SRSactivation based on an UL SA DCI format, according to an embodiment ofthe present invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE PRESENT INVENTION

Embodiments of the present invention are described in detail withreference to the accompanying drawings. The same or similar componentsmay be designated by the same or similar reference numerals althoughthey are illustrated in different drawings. Detailed descriptions ofconstructions or processes known in the art may be omitted to avoidobscuring the subject matter of the present invention.

Although the present invention is described in relation to an OrthogonalFrequency Division Multiple Access (OFDMA) communication system, it mayalso apply to all Frequency Division Multiplexing (FDM) systems ingeneral and to Single-Carrier Frequency Division Multiple Access(SC-FDMA), Orthogonal Frequency Division Multiplexing (OFDM), FrequencyDivision Multiple Access (FDMA), Discrete Fourier Transform (DFT)-spreadOFDM, DFT-spread OFDMA, Single-Carrier-OFDMA (SC-OFDMA), andSingle-Carrier-OFDM (SC-OFDM), in particular.

The embodiments of the present invention relate todynamic activation anddeactivation of SRS transmissions in a UL CC with configured SRStransmissions for a reference UE, dynamic configuration of SRStransmission parameters, dynamic or semi-static activation andconfiguration of SRS transmissions in a UL CC without configured SRStransmissions, and dynamic configuration of SRS transmission parametersfrom multiple UE antennas.

The dynamic activation and deactivation of SRS transmissions uses atleast one UL SA DCI format from the UL SA DCI formats a UE decodes. Theactivated SRS transmission may occur either once or indefinitely untildisabled.

The dynamic configuration of the SRS transmission parameters, such as,for example, the period, the BW, the comb, and the CS, may occur eitheronce or indefinitely until disabled.

A first method to activate or deactivate SRS transmissions using a UL SADCI format includes a 1-bit “SRS Activation” IE. The UE, upon receptionof the UL SA DCI format, examines the value of the “SRS Activation” IE.For example, “SRS Activation”=0 may indicate deactivation of an existingSRS transmission or to maintain the absence of SRS transmissions. “SRSActivation”=1 may indicate activation of SRS transmissions or maintainan existing SRS transmission using previously assigned parametersthrough higher layer signaling. Activated SRS transmissions may occuronce or indefinitely until disabled. Activated SRS transmissionsoccurring once can be in a UL CC without configured SRS transmissions.

If the UE has more than one transmitter antenna, SRS activation mayapply to only a subset of these antennas. A first method for indicatingactivation of multiple antenna subsets is through explicit signaling.The number of bits in the “SRS Activation” IE should be such that theycan address all possible antenna subsets. For example, for a UE with twoor four transmitter antennas, a 2-bit “SRS Activation” IE can beinterpreted by the UE as in Table 3. The same principle can be extendedto a larger number of UE transmitter antennas.

TABLE 3 Explicit SRS Activation. SRS Activation UE Action UE Action IE(2 Transmitter Antennas) (4 Transmitter Antennas) 00 No SRS ActivationNo SRS Activation 01 SRS Activation for Antenna SRS Activation forAntennas 1 1 and 2 10 SRS Activation for Antenna SRS Activation forAntennas 3 2 and 4 11 SRS Activation for all SRS Activation for allAntennas Antennas

The UE action is illustrated in FIG. 9, assuming that there are 4 UEtransmitter antennas. The UE, upon the signal reception 910, decodes theUL SA DCI format in block 920, and examines the value of the “SRSActivation” IE in block 930. If the value is 00, the SRS is notactivated (or an active SRS is deactivated) as shown in block 940. Ifthe value is 01, the UE begins SRS transmission, using previouslyconfigured parameters, from antenna 1 and antenna 2, as shown in block950. If the value is 10, the UE begins SRS transmission, usingpreviously configured parameters, from antenna 3 and antenna 4, as shownin block 960. If the value is 11, the UE begins SRS transmission, usingpreviously configured parameters, from all four antennas, as shown inblock 970.

A second method to activate or deactivate SRS transmissions frommultiple UE transmitter antenna subsets through a UL SA DCI formatutilizes combinations of explicit and implicit signaling. The 1-bit “SRSActivation” IE can be combined with another IE under some restrictionsin the addressable range of the latter IE. For example, when combiningthe “SRS Activation” IE with the “CQI Request” IE, their combination canbe interpreted as shown in Table 4. The restriction is that positive CQIrequests and SRS activation cannot occur simultaneously with the same ULSA DCI format and independent activation of the subset of {antenna 3,antenna 4}, in case of 4 UE transmitter antennas, is also not possible.

Nevertheless, the most significant configurations, as well as the caseof 2 UE transmitter antennas, can be addressed while reducing the numberof bits required in the UL SA DCI format by one, relative to fullexplicit signaling.

TABLE 4 Combining Interpretation of CQI Request IE and SRS ActivationIE. CQI Request IE SRS Activation UE Action UE Action IE (2 TransmitterAntennas) (4 Transmitter Antennas) 00 No CQI Request - No No CQIRequest - No SRS SRS Activation Activation 01 No CQI Request - SRS NoCQI Request - SRS Activation Activation for Antenna 1 for Antennas 1 and2 10 CQI Request - No SRS CQI Request - No SRS Activation Activation 11No CQI Request - SRS No CQI Request - SRS Activation Activation for allfor all Antennas Antennas

Another combination of explicit and implicit signaling for SRSactivation utilizes the I_(MCS) values of the MCS IE. IncrementalRedundancy (IR) with four Redundancy Versions (RVs), RV0, RV1, RV2, andRV3, is assumed to apply for the HARQ process. To maximize separation ofthe RVs, and therefore maximize the respective coding gain for each HARQtransmission, the order of the RVs may be {RV0, RV2, RV3, RV1}, with RV0corresponding to an initial packet transmission. Then, for synchronousUL HARQ, the last 3 values of the 5-bit MCS IE may indicate one of the 3RVs for a retransmission with the MCS being determined from the mostrecent PDCCH for the same transport block. Therefore, 0≦I_(MCS)≦28indicates a valid MCS for a new packet transmission while, forretransmissions, RV2, RV3, and RV1 are respectively indicated byI_(MCS)=29, I_(MCS)=30, and I_(MCS)=31. Since RV1 and RV3 are used leastfrequently for retransmissions, they can be combined with the “SRSActivation” IE, whenever the latter indicates SRS transmission, toaddress antenna subsets as in the arrangement shown in Table 5. Theinability to use RV1 or RV3 whenever “SRS Activation”=1 results innegligible loss in system throughput.

TABLE 5 Combining Interpretation of MCS IE and SRS Activation IE. MCSSRS UE Action IE Activation (2 Transmitter UE Action I_(MCS) IEAntennas) (4 Transmitter Antennas) Any 0 No SRS Activation No SRSActivation Any 1 SRS Activation for SRS Activation for Antennas 1Antenna 1 and 2 31 1 SRS Activation for SRS Activation for all allAntennas Antennas 30 1 SRS Activation for SRS Activation for Antennas 3Antenna 2 and 4

Modifications to the embodiments in Table 3, Table 4, and Table 5 can beapplied. For example, for two UE transmitter antennas in Table 5, theMCS entry I_(MCS)=30 may not be used at all. Instead SRS activation fortransmitter antenna 1 may always apply whenever SRS transmission isenabled. Moreover, in all previous cases, SRS transmission can bedisabled through the UL SA DCI format by having “SRS Activation”=0.

For a UE with multiple transmitter antennas, it is also possible for theSRS transmission to begin without explicit activation once the SRStransmission parameters are configured through higher layer (MAC or RRC)signaling. However, SRS transmission from only one antenna at each SRStransmission instance is assumed in this case, thereby possiblyalternating among antennas in successive SRS transmission instances. Forexample, antenna 1 may be used in a first SRS transmission instance,antenna 2 may be used in the next SRS transmission instance, and so on.Activation of SRS transmissions from antenna subsets occurs as describedabove. Table 6 shows the explicit SRS activation from multiple antennasusing a 1-bit “SRS Activation” IE. Table 7 shows an example of explicitand implicit SRS activation from multiple antennas using a 1-bit “SRSActivation” IE.

TABLE 6 Explicit SRS Activation for Multiple Antennas (InitialTransmission from 1 Antenna). SRS Activation UE Action UE Action IE (2Transmitter Antennas) (4 Transmitter Antennas) 0 No further SRSActivation No further SRS Activation 1 SRS Activation for all SRSActivation for all Antennas Antennas

TABLE 7 Combining MCS IE and SRS Activation IE (Initial SRS Transmissionfrom 1 Antenna). MCS IE SRS Activation UE Action I_(MCS) IE (4Transmitter Antennas) Any 0 No SRS Activation Any 1 SRS Activation forAntennas 1 and 2 31 1 SRS Activation for all Antennas

The UE action when there is a combination of explicit and implicitsignaling, or when implicit signaling is used for SRS activation, can bederived in a straightforward manner from that described with respect toFIG. 9.

Dynamic configuration of SRS transmission parameters in a UL CC withalready configured SRS transmissions or in a UL CC without configuredSRS transmissions utilizes at least one of the possibly multiple UL SADCI formats a reference UE is assumed to decode. For a UL CC with aconfigured SRS transmission, the dynamic configuration of the SRStransmission parameters overrides the previously configured SRStransmission parameters. For a UL CC without a configured SRStransmission, the dynamic configuration of the SRS transmissionparameters also serves as an activation of the SRS transmission.

When configuring the SRS transmission parameters, the UL SA DCI formatis not interpreted as scheduling a packet transmission, but rather asconfiguring an SRS transmission. This configuration can be performedeither explicitly, using an “SRS Activation” IE, or implicitly, usingcertain values in existing IEs. For example, with respect to an implicitindication, the UL SA DCI format may be interpreted as configuring anSRS transmission if the “CQI Request” IE equals 1 and the “MCS” IEI_(MCS) equals 30 or 31. With respect to an explicit indication, the ULSA DCI format may be interpreted as configuring an SRS transmission ifthe “SRS Activation” IE equals 1; otherwise, if the “SRS Activation” IEequals 0, the SRS transmission remains as previously configured byhigher layer (MAC or RRC) signaling. Considering the UL SA DCI format inTable 1 and the inclusion of an “SRS Activation” IE (this IE is notneeded with implicit configuration of the SRS transmission parameters),the UL SA DCI format contents may be interpreted as shown in Table 8.

TABLE 8 IEs for Configuring SRS Transmission through an UL SA DCIFormat. Information IE Number of Bits Comment SRS Activation 1 UL SAactivates SRS transmission (Yes/No) SRS 2 × N_(ant) Four SRS BWs peroperating BW Transmission BW SRS Starting 5 × N_(ant) Starting SRS BWPosition BW SRS 1 × N_(ant) Two combs Transmission Comb SRS Cyclic 3 ×N_(ant) Eight cyclic shifts Shift SRS 3 × N_(ant) Transmissionperiodicity (in Transmission sub-frames) Period SRS Starting 8 × N_(ant)Starting sub-frame (one of 256 Sub-frame sub-frames) SRS Hopping 1 ×N_(ant) SRS BW Hopping TPC Command 2 × N_(ant) Transmission powercontrol command UL Component 2 × N_(ant) Maximum of 4 UL ComponentCarriers Carrier CRC (UE ID) 16 UE ID masked in the CRC TOTAL 17 + 27 ×N_(ant)

The “SRS Activation” IE and the CRC field do not depend on the number ofUE transmitter antennas. The remaining IEs may apply per UE transmitterantenna to provide full flexibility. However, for more than one UEtransmitter antenna, the total size of the UL SA DCI format configuringSRS transmissions may become larger than the one for scheduling datapacket transmissions. Additionally, flexibility to configure independentSRS transmission parameters for each antenna is usually not needed. Toavoid increasing the UL SA DCI format size for configuring SRStransmissions as the number of UE transmitter antennas increases,embodiments of the present invention consider several restrictions andsimplifications.

For SRS transmission from multiple UE antennas, the same BW for allantennas can be used. Therefore, embodiments of the present inventionconsider that the SRS transmission BW, the SRS starting BW location, theSRS hopping activation, and the UL CC of SRS transmission are specifiedfor one UE transmitter antenna and are the same for the remaining UEtransmitter antennas.

Alternatively, these SRS transmission parameters may be derivedaccording to a predetermined rule relative to those specified throughthe UL SA DCI format for the reference transmitter antenna. For example,to support transmission antenna diversity when the transmissions fromtwo UE antennas are correlated, the starting SRS transmission BW for thesecond antenna may be that which is furthest from the starting SRStransmission BW for the first antenna. Regardless of the exactrelationship between the previous SRS parameters for the UE transmitterantennas, embodiments of the present invention consider that they areonly signaled for one UE transmitter antenna.

Other SRS transmission parameters that may be common among all UEtransmitter antennas are the SRS transmission period and the SRSstarting transmission sub-frame. This is due to the fact that it isbeneficial for the Node B scheduler to be provided with a UL CQIestimate for each UE transmitter antenna at the same time. Otherwise,the UL CQI reliability may be different among antennas as the UL channelvaries with time, which may degrade the UL spectral efficiency.Additionally, a reduced range for the configuration of these parameters,relative to those already configured through higher layer (MAC or RRC)signaling, may apply. For example, higher layer signaling configures theSRS starting transmission sub-frame using 8 bits, but the adjustmentwith the subsequent configuration is with 4 bits to inform 1 of 16possible predetermined sub-frame locations relative to the previousconfigured sub-frame.

The previous restrictions in the SRS transmission parameters frommultiple UE transmitter antennas may also apply if higher layer (MAC orRRC) signaling is used to configure these parameters and SRS activationis either immediate upon configuration or is enabled subsequentlythrough a UL SA DCI format. Higher layer (MAC or RRC) signaling may onlyspecify the SRS transmission parameters for one reference UE transmitterantenna and the SRS transmission parameters for the remaining UEtransmitter antennas may be the same or derived in a predeterminedmanner from those for the reference UE transmitter antenna.

Regarding the SRS CS and SRS transmission comb, it may often bebeneficial to allow their specification through respective IEs in the ULSA DCI format configuring the SRS transmission. This is due to the factthat SRS transmissions from other UEs may already exist in the same BWand the same sub-frame when SRS transmissions from the reference UE needto be configured. SRS collisions may be avoided by assigning a differentCS or comb to the SRS transmissions from the reference UE. This optionis possible when the number of bits in the UL SA DCI format configuringthe SRS transmission parameters is adequately large.

Regarding the SRS TPC command, different UE transmitter antennas mayexperience different shadowing conditions leading to the requirement fordifferent adjustments of the respective transmission power. However, asthe different shadowing conditions among UE transmitter antennas remainconstant over much longer periods than the sub-frame period, therespective power control adjustments can be made through higher layers(MAC or RRC) and only a single TPC command applicable to all UEtransmitter antennas may be included in the DCI format configuring theSRS transmission parameters.

When the number of bits in the UL SA DCI format configuring the SRStransmission parameters is not adequately large, only the CS and thecomb for the SRS transmission from the first antenna may be explicitlysignaled, while the respective parameters for the remaining antennas areimplicitly derived from those for the first antenna. For example, for aUE with 2 transmitter antennas, if a first CS value, from a set ofpossible CS values, is explicitly signaled for the SRS transmission fromthe first antenna, the CS value for the SRS transmission from the secondantenna can be the same as the CS value for the SRS transmission fromthe first antenna when a different comb is used, can be the next CSvalue from the set of CS values, or can be the CS value, from the set ofCS values, that is separated the most from the signaled CS value.Similarly, the comb for the SRS transmission from the second antenna canbe the same as the comb for the SRS transmission from the first antennawhen different CS values are used or, assuming two possible comb values,if the SRS transmission from the first antenna uses the first comb valuethe SRS transmission from the second antenna uses the second comb value.

Based on the previous restrictions and simplifications, the UL SA DCIformat content for the configuration of the SRS transmission parametersmay be interpreted as shown in Table 9 with respect to one of the UEtransmitter antennas.

TABLE 9 Configuring SRS Transmission through an UL SA DCI Format. NumberSRS Information IE of Bits Comment SRS Activation 1 Interpretation of ULDCI format SRS Transmission 2 Four SRS BWs per operating BW BW SRSStarting BW 5 Starting BW Position (3 bits are enough for 5 MHz) SRSTransmission 1 Two combs Comb SRS Cyclic Shift 3 Eight cyclic shifts SRSTransmission 3 or less For reduced range, value is relative to Periodprevious one SRS Starting Sub- 8 or less For reduced range, value isrelative to Frame previous one SRS Hopping 1 Hopping On/Off SRS TPCCommand 2 Transmission power control command UL Component 2 Indicate 1of 4 (pre-configured) UL CCs Carrier CRC (UE ID) 16  UE ID masked in theCRC TOTAL 44 or less

If the SRS CS and SRS comb are explicitly signaled for all UEtransmitter antennas, the UL SA DCI format content for the configurationof the SRS transmission parameters may be interpreted as shown in Table10 with respect to one of the UE transmitter antennas.

TABLE 10 Configuring SRS Transmission through an UL SA DCI Format. SRSCS and SRS Comb are Explicitly Signaled for each UE Transmitter Antenna.SRS Information IE Number of Bits Comment SRS Activation 1Interpretation of UL DCI format SRS 2 Four SRS BWs per operating BWTransmission BW SRS Starting BW 5 Starting BW Position (3 bits areenough for 5 MHz) SRS Transmission 1 × N_(ant) Two combs Comb SRS CyclicShift 3 × N_(ant) Eight cyclic shifts Sub-Frame Offset 8 or less Forreduced range, value is relative to previous one SRS Transmission 3 orless For reduced range, value is Period relative to previous one SRSHopping 1 Hopping On/Off SRS TPC Command 2 Transmission power controlcommand UL Component 2 Indicate 1 of 4 (pre-configured) Carrier UL CCsCRC (UE ID) 16  UE ID masked in the CRC TOTAL ≦38 + 4 × N_(ant)

The UE may choose the transmitter antenna for which the SRS transmissionparameters are specified, and the Node B may not have knowledge of theUE transmitter antenna for which it specifies the SRS transmissionparameters. Moreover, although the previous implicit configuration ofthe SRS transmission parameters was described assuming physical layercontrol signaling (through a DCI format), the same principles apply forhigher layer control signaling, such as MAC signaling or RRC signaling.

The configured SRS transmission may be in the same UL CC as an existingSRS transmission. In this case, configuration of the SRS transmissionparameters may serve to more effectively utilize the available resourcesand minimize the associated SRS overhead. For example, the Node B candynamically disable SRS hopping if good SINR is obtained in a particularpart of the BW, or can dynamically enable SRS hopping when the oppositeoccurs. Also, the Node B can dynamically reassign SRS transmissionresources that become available to other UEs in order to improve SRSmultiplexing capacity and reduce the corresponding overhead, or canincrease the SRS transmission BW as the UE SINR increases (and thereverse).

If the configured SRS transmission corresponds to a UL CC without anexisting SRS transmission, the SRS transmission may be a single,“one-shot”, transmission that serves to provide an estimate of theinterference and channel conditions the reference UE may experience inthe new UL CC. Based on this information, the serving Node B may thendecide to transition the PUSCH transmission from the reference UE to thenew UL CC to incorporate the new UL CC in those with configured PUSCHtransmission, or to decide against configuring the new UL CC for PUSCHtransmissions. The reference UE is assumed to know the numbering of theUL CCs, for example, through previous higher layer (MAC or RRC)signaling. The configuration of the SRS transmission parameters in a ULCC without an existing SRS transmission may also be semi-static throughhigher layer signaling. The previously described DCI formatconfiguration of the SRS transmission parameters is again provided usinghigher layer signaling.

For the configuration of the SRS transmission parameters in a UL CCwithout an existing SRS transmission, not all IEs in Table 8, Table 9,or Table 10 need to be specified since there is no need to provideinformation about SRS activation, SRS hopping, and SRS transmissionperiodicity (single SRS transmission is assumed). For the SRStransmission sub-frame, no specification may apply when a fixed offsetapplies between the sub-frame of the DCI format transmission and thesub-frame of the SRS transmission. For example, the sub-frame of SRStransmission may immediately follow that of the UL SA DCI formatreception. However, to provide some flexibility, a small number of bits,such as 3 bits, can be used to specify that the sub-frame may bespecified relative to the first UL sub-frame after the UL SA DCI formatreception. Also, transmission may be preconfigured to be only from asubset of the set of UE transmitter antennas, and not from all UEtransmitter antennas.

Explicit indication of the CS and the comb may then apply by utilizingthe unused IEs. The UE then interprets the bits corresponding to theseIEs differently depending on whether the UL CC for which the SRStransmission parameters are configured already has an SRS transmission(the IEs convey their respective information), or not (the bits of thoseIEs can convey the CS or the comb for multiple transmitter antennas).Additionally, power control commands for the transmission of the SRS inthe UL CC without an existing SRS transmission may be included in theDCI format. Table 11 summarizes the above reinterpretation aspects. Ingeneral, if the number of bits required for configuring the parametersfor SRS transmission in a UL SA DCI format are fewer than the number ofbits in that UL SA DCI format, each of the remaining bits can be set toa respective pre-determined value such as zero. The information in Table11 may also be provided by higher layer (MAC or RRC) signaling.

TABLE 11 Configuring SRS Transmission in UL CC without Configured SRSTransmission. Number of SRS Information IE Bits Comment SRS Transmission2 Four SRS BWs per operating BW BW SRS Starting BW 5 Starting BWPosition (3 bits are enough for 5 MHz) SRS Transmission ≦1 × N_(ant) Twocombs (not all antennas Comb may be used) SRS Cyclic Shift ≦3 × N_(ant)Eight cyclic shifts (not all antennas may be used) Sub-Frame Offset 3Specify UL Sub-frame SRS TPC Command 2 Power control command relative tolast SRS transmission UL Component 2 Indicate 1 of 4 (pre-configured)Carrier UL CCs CRC (UE ID) 16  UE ID masked in the CRC TOTAL ≦30 + 4 ×N_(ant)

While the present invention has been shown and described with referenceto certain embodiments thereof, it will be understood by those skilledin the art that various changes in form and detail may be made thereinwithout departing from the spirit and scope of the present invention asdefined by the appended claims.

What is claimed is:
 1. In a communication system wherein a base stationtransmits a Downlink Control Information (DCI) format conveying aScheduling Assignment (SA) to a User Equipment (UE), the DCI formatincluding Information Elements (IEs) configuring transmission of datainformation from the UE to the base station, the IEs including binaryelements, a method to activate transmission of Reference Signals (RSs)from the UE, the method comprising: including in the DCI format an “RSActivation” IE including two binary elements if a data transmission isfrom multiple UE transmitter antennas; including in the DCI format an“RS Activation” IE including one binary element if a data transmissionis from a single UE transmitter antenna; and transmitting the DCI formatin which the “RS Activation” IE is included to the UE.
 2. The method ofclaim 1, wherein the UE transmits an RS once.
 3. The method of claim 1,wherein if an RS transmission triggered by the “RS Activation” IE is tooccur at a same instance as an RS transmission of a same type that waspreviously configured to the UE from the base station to occurperiodically, the UE transmits only an RS triggered by the “RSActivation” IE.
 4. The method of claim 1, wherein the parameters of RStransmission are configured to the UE from the base station throughhigher layer signaling.
 5. In a communication system wherein a basestation transmits a Downlink Control Information (DCI) format conveyinga Scheduling Assignment (SA) to a User Equipment (UE), the DCI formatincluding Information Elements (IEs) configuring transmission of datainformation from the UE to the base station, the IEs including binaryelements, a method to activate transmission of Reference Signals (RSs)from the UE, the method comprising: receiving, from the base station,the DCI format in which an “RS Activation” IE including two binaryelements is included if a data transmission is from multiple UEtransmitter antennas; and receiving, from the base station, the DCIformat in which an “RS Activation” IE including one binary element isincluded if a data transmission is from a single UE transmitter antenna.6. The method of claim 5, wherein the UE transmits an RS once.
 7. Themethod of claim 5, wherein if an RS transmission triggered by the “RSActivation” IE is to occur at a same instance as an RS transmission of asame type that was previously configured to the UE from the base stationto occur periodically, the UE transmits only an RS triggered by the “RSActivation” IE.
 8. The method of claim 5, wherein the parameters of RStransmission are configured to the UE from the base station throughhigher layer signaling.
 9. A base station in a communication systemwherein the base station transmits a Downlink Control Information (DCI)format conveying a Scheduling Assignment (SA) to a User Equipment (UE),the DCI format including Information Elements (IEs) configuringtransmission of data information from the UE to the base station, theIEs including binary elements, the base station comprising: a configurerfor including in the DCI format a “Reference Signal (RS) Activation” IEincluding two binary elements if a data transmission is from multiple UEtransmitter antennas, and including in the DCI format an “RS Activation”IE including one binary element if a data transmission is from a singleUE transmitter antenna; and a transmitter for transmitting the DCIformat in which the “RS Activation” IE is included to the UE.
 10. Thebase station of claim 9, wherein the UE transmits an RS once.
 11. Thebase station of claim 9, wherein if an RS transmission triggered by the“RS Activation” IE is to occur at a same instance as an RS transmissionof a same type that was previously configured to the UE from the basestation to occur periodically, the UE transmits only an RS triggered bythe “RS Activation” IE.
 12. The base station of claim 9, wherein theparameters of RS transmission are configured to the UE from the basestation through higher layer signaling.
 13. A User Equipment (UE) in acommunication system wherein a base station transmits a Downlink ControlInformation (DCI) format conveying a Scheduling Assignment (SA) to theUE, the DCI format including Information Elements (IEs) configuringtransmission of data information from the UE to the base station, theIEs including binary elements, the UE comprising: a receiver forreceiving, from the base station, the DCI format in which a “ReferenceSignal (RS) Activation” IE including two binary elements is included ifa data transmission is from multiple UE transmitter antennas, andreceiving, from the base station, the DCI format in which an “RSActivation” IE including one binary element is included if a datatransmission is from a single UE transmitter antenna.
 14. The UE ofclaim 13, wherein the UE transmits an RS once.
 15. The UE of claim 13,wherein if an RS transmission triggered by the “RS Activation” IE is tooccur at a same instance as an RS transmission of a same type that waspreviously configured to the UE from the base station to occurperiodically, the UE transmits only an RS triggered by the “RSActivation” IE.
 16. The UE of claim 13, wherein the parameters of RStransmission are configured to the UE from the base station throughhigher layer signaling.